I was using some of my textures to create custom plants today, when it occured to me that the plants I had created changed color hues when I generated variants.

These three plants use different textures, but their colors are near identical. They should look the same, but Vue alters their color tone and they are slightly different.

I have seen the SolidGrowth Solid Color Plants video tutorial, but it only works for plants having different leaf subsets. My plant only has one.

Is there a way to prevent or control those color changes?

If not this should really be added in the next version of Vue.
I understand that SolidGrowth tries to create variants of the plants, but in the real world, plant colors do not vary that much from one individual to another, within the same specie.

There is a way to have control on the randomness Vue creates in the colors of plants. Chippwalters has a great tut on that (and on several other things), in his site, direct link here:
http://www.altuit.com/webs/altuit2/VueTraining/Vodcasts.htm

This is the tutorial I had seen.

Unfortunately, it does not work for me as my plant only have one leaf subset. I suppose it is yet another issue than the one addressed by the tutorial.

Chipp's tutorial only works with plants that have empty subsets.
Solidgrowth means that each plant is different from the previous one, be it in size, shape AND colour. Some plants have embedded colour variation, like the coconut that turns red sometimes, or the Mexican palm that has grey dead leaves sometimes. And there is not much yu can do about it. The only  possibility is to keep generating new plants in the plant editor, until you get one that has no or minimum colour variation, and then save this one as a new species. Sometimes, it will work, but sometimes the variation will come back.

Well, there is always the possibility to save a certain plant as VOB and then duplicate it or use it in an ecosystem, changing size, rotation angle and tilt angle to simulate shape diversity, but keeping same colors (like in other 3D apps).
Or, of course, to have a bigger diversity, you can keep generating until you get 3 or 4 plants with similar tone (but different branch arrangement), save each one as VOB and use it in an ecosystem, with size and rotation change. This should provide enough shape diversity.

But I think you are right, this is something that definitely e-on should consider in a next version. 

You're absolutely right, Artur, and even if saved as vob, Vue will recognize the object is a plant, and it will still react to breeze and wind.